Ankylosing spondylitis (AS), rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) are the most common rheumatic diseases dealt with rheumatologists in Taiwan. In previous studies, the 3 diseases all have broad impacts on health-related quality of life of patients and drive enormous economic burden on patients and society. The objective of this study is to compare health-related quality of life and disease-related costs between patients with the 3 different diseases.